The present invention generally relates to an automatic implantable atrial defibrillator for delivering cardioverting or defibrillating electrical energy to the atria of a human heart. The present invention is more particularly directed to such an atrial defibrillator which delays therapy intervention for a delay period once atrial fibrillation is originally detected to provide the heart with an opportunity to self-revert to normal sinus rhythm before cardioverting electrical energy is applied to the atria to cardiovert the heart.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly and many times can only be corrected by a discharge of electrical energy to the heart through the skin of the patient by way of an external defibrillator of the type well known in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the heart in synchronism with a detected electrical activation (R wave) of the heart. The treatment is very painful and, unfortunately, most often only results in temporary relief for patients, lasting but a few weeks.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistant to them which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of these atrial defibrillators have become a commercial reality.
Implantable atrial defibrillators proposed in the past have exhibited a number of disadvantages which probably has been the cause of these defibrillators from becoming a commercial reality. Two such defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting the heart. Both of these defibrillators require the patient to recognize the symptoms of atrial fibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator requiring the patient to activate the defibrillator from external to the patient's skin with a magnet.
Implantable ventricular defibrillators for applying defibrillating electrical energy to the ventricles of the heart are well known and have been commercially available for a number of years. Ventricular fibrillation is life threatening, resulting in unconsciousness in just a few seconds and leading to death in just a few minutes. Hence, implantable ventricular defibrillators must be fully automatic for detecting ventricular fibrillation and quickly, without delay, providing defibrillating therapy to the ventricles when ventricular fibrillation is detected. The amount of energy required to cardiovert or defibrillate the ventricles with implantable devices has been on the order of ten joules or more. At such energies, cardioversion can be extremely painful and traumatic. Fortunately, or unfortunately, when patients are being cardioverted for ventricular fibrillation, they are generally already unconscious.
Episodes of atrial fibrillation occur much more frequently than do episodes of ventricular fibrillation, and patients do not normally lose consciousness as a result of their atrial fibrillation. Even though the energies required to cardiovert or defibrillate the atria have been reduced to a few joules or less, cardioversion even at these energy levels can be perceived by patients as being painful, or at least causing discomfort. Hence, any reduction in the number of required cardioversions of a patient would be considered desirable.
The present invention addresses the issue of decreasing the number of required atrial cardioversions by an implantable atrial defibrillator. This not only serves to obviate unrequired cardioversion to limit patient discomfort, but additionally serves to lengthen the useful life of an atrial defibrillator by conserving energy. The atrial defibrillator of the present invention achieves these goals by taking advantage of the fact that in some atrial fibrillation patients, some of their atrial fibrillation episodes will spontaneously revert to normal sinus rhythm within some reasonable time period from initial episode onset. In these cases, although immediate cardioversion would most likely be successful, such immediate intervention or therapy would also have been unnecessary. Hence, the number of cardioversion attempts can be reduced without compromising the patient as long as the atrial fibrillation episodes are not permitted to persist too long.